prop_number(3) and portability of externalized plists

Hi,
I'm bothered by the unconventional (for a Apple plists anyway) encoding
of unsigned integers in externalized proplib(3) plists.
At least Python's plistlib is unequiped to handle internalizing and
reexternalizing such numbers in base-16.
Is there a reason we absolutely need to have this
contrary-to-comment-in-Apple's-DTD encoding?
It seems to me that the unsigned attribute does not need to be
exposed outside of proplib. When proplib internalizes a number
beyond INT64_MAX it can mark it as unsigned, and thus then later
externalize it as the same base-10 number. The only difference I
can see such a change making is prop_number_unsigned(3) would
only claim a number beyond INT64_MAX was unsigned, but this
does not seem like it would be relied upon in existing code.
Jonathan Kollasch